Fenretinide-induced apoptosis of human head and neck squamous carcinoma cell lines

PPAR Activation and Decreased Proliferation in Oral Carcinoma Cells With 4-HPR

OBJECTIVE: To explore whether the mechanism of action of 4-hydroxyphenylretinamide (4-HPR, fenretidine), a synthetic retinoid, involves the functional activation of the nuclear hormone receptor class known as PPARs (peroxisome proliferator-activated receptors). Also, to examine whether anti-proliferative effects of this agent in head and neck cancer cells occur at biologically relevant concentrations.

STUDY DESIGN/METHODS: CA 9–22, NA, and UM SCC 11B cells were treated with 4-HPR during their log phase growth and functional activation of PPAR γ was evaluated by plate luminometry. Cellular proliferation was analyzed by standard MTT cell proliferation assays and cell counting. Student's t tests were performed for all experiments.

RESULTS: Significant dose-dependent increases in PPAR γ activation occurred in response to 4-HPR treatment. Proliferation was significantly inhibited by 4-HPR in a dose-dependent manner as judged by MTT and cell counting assays. These effects occurred at equimolar concentrations in both types of experiments within a range of clinically achievable doses (1–4 μM) of 4-HPR.

CONCLUSIONS: 4-HPR can functionally activate PPAR γ at clinically achievable doses. Decreased cancer cell proliferation secondary to PPAR γ activation has been observed in other malignancies as well as upper aerodigestive cancer. PPAR γ activation by 4-HPR represents another potential anti-cancer mechanism of action for this drug.

CLINICAL SIGNIFICANCE: PPAR γ activation represents a novel target for anti-cancer therapy for head and neck cancer and the current level of clinical toxicity of 4-HPR would be judged acceptable to utilize this agent alone or in combination chemotherapy.

Fenretinide Perturbs Focal Adhesion Kinase in Premalignant and Malignant Human Oral Keratinocytes. Fenretinide's Chemopreventive Mechanisms Include ECM Interactions

The membrane-associated protein, focal adhesion kinase (FAK), modulates cell-extracellular matrix interactions and also conveys prosurvival and proliferative signals. Notably, increased intraepithelial FAK levels accompany transformation of premalignant oral intraepithelial neoplasia (OIN) to oral squamous cell carcinoma (OSCC). OIN chemoprevention is a patient-centric, optimal strategy to prevent OSCC's comorbidities and mortality. The cancer chemopreventive and synthetic vitamin A derivative, fenretinide, has demonstrated protein-binding capacities, for example, mTOR- and retinol-binding protein interactions. These studies used a continuum of human oral keratinocytes (normal-HPV E6/E7-transduced-OSCC) to assess potential fenretinide-FAK drug protein interactions and functional consequences on cellular growth regulation and motility. Molecular modeling studies demonstrated that fenretinide has approximately 200-fold greater binding affinity relative to the natural ligand (ATP) at FAK's kinase domain. Fenretinide also shows intermediate binding at FAK's FERM domain and interacts at the ATP-binding site of the closest FAK analogue, PYK2. Fenretinide significantly suppressed proliferation via induction of apoptosis and G2-M cell-cycle blockade. Fenretinide-treated cells also demonstrated F-actin disruption, significant inhibition of both directed migration and invasion of a synthetic basement membrane, and decreased phosphorylation of growth-promoting kinases. A commercially available FAK inhibitor did not suppress cell invasion. Notably, although FAK's FERM domain directs cell invasion, FAK inhibitors target the kinase domain. In addition, FAK-specific siRNA-treated cells showed an intermediate cell migration capacity; data which suggest cocontribution of the established migrating-enhancing PYK2. Our data imply that fenretinide is uniquely capable of disrupting FAK's and PYK2's prosurvival and mobility-enhancing effects and further extend fenretinide's chemopreventive contributions beyond induction of apoptosis and differentiation.

Impact of apigenin and kaempferol on human head and neck squamous cell carcinoma

OBJECTIVE

Apigenin and kaempferol are plant flavonoids with reported chemopreventive activities. This study aimed to determine the effect of apigenin and kaempferol on cell viability in cultured cells derived from the pharynx (FaDu cell line), an oral cavity carcinoma (PCI-13 cell line), and a metastatic lymph node (PCI-15B cell line) and in explanted FaDu cells.

STUDY DESIGN

The in vitro viability of FaDu, PCI-13, and PCI-15B cells treated with apigenin and kaempferol was determined. Tumor growth of FaDu explants was evaluated in athymic mice that were gavaged with either apigenin or kaempferol.

RESULTS

Although apigenin and kaempferol treatment decreased viability of cells in vitro, cell-type-dependent differences in responsiveness were observed. In vivo apigenin treatment significantly increased the tumor size of FaDu explants. Results obtained using kaempferol were similar.

CONCLUSIONS

The in vitro decrease in FaDu cell viability by apigenin and kaempferol was not observed in in vivo tumor explants using the conditions described in this study.